Play the RBY Lavender Town song and right after it play the FRLG version. It's pretty awesome and creepy sounding. I was pretty eerie for me as a kid. I would get out of Lavender Town as quick as I could, not wanting to hear it.

Someone in Youtube comments wrote this about Hypno and it makes it all the more creepy:

Come little children come with meSafe and happy you will beAway from you're homes now let us runWith Hypno you'll have so much fun

Oh little children please don't cryHypno wouldn't hurt a flyBe free, be free, be﻿ free, to playCome down in my cave with me to stay

Oh little children please don't squirmThose ropes I know will hold you firmHypno tells you this is trueBut sadly Hypno lied to you

Oh little children you musn't leaveYour families for you will grieveTheir minds will unravel at﻿ the seamsAllowing me to haunt their dreams

But surely all of you must knowThat it is time for you to goOh little children you weren't cleverNow you shall stay with me forever.

Serious, if you read up on drowzee and hypno they're like Freddy Krueger.